Ok, I don't know about anybody else on here, but there has been several time where I/my other half have either killed or nearly killed the battery because the lights were left on when we got out of the car.
Now, I've just finished fitting something to my car to act as a warning when the lights are left on, which, is such an incredibly simple (could be even simpler too) method of creating a warning which I was that impressed with, I felt it necessary to share.
Quite simply, I created a circuit which incorporates a buzzer hidden away under the dash which when the lights are left on, and ignition is off, the buzzer will sound as a reminder.
The circuit is simple, works and made using odds and sods in my components bin.
Also, the potentiometer is used as feedback between the output, input and capacitor to make the opamp oscillate. If the pot is varied in resistance, then the output varies also meaning the tone of the piezo varies too from a low hum, all the way to a squeel beyond your hearing range so you can choose something that's the most pleasant.
First off, the circuit itself.
If you head over to
http://tinyurl.com/4478sq8 it'll run a Java app which shows the circuit in detail.
How does the circuit work? The PNP transistor does most of the work here. The base of the transistor is pulled low by the 100k resistor turning the transistor on. If the ignition is on, then there is a voltage on the base of the PNP turning the transistor off regardless of the pulldown. When the transistor is on and the headlights are on, this mean the rest of the circuit is provided with power so long as the +ive and -ive supply pins of the opamp are connected to 12v and ground respectively.
The opamp in this case is an LME49710 (free sample from national.com) and is wired up to make it oscillate, the output of which is enough to power a small piezo or buzzer and because power and trigger is supplied by the transistor, when the headlights/ignition are both off it doesn't draw any power.
This picture shows the wiring coming from the ignition, familiar sight no?
My plan was to use a series of piggybacks as there were several wires coming off the single original cable which is the black and blue one which is only live when the ignition is on.
Afterwards, a series of piggybacks. It's not pretty, but got to be better than soldering wires on top of each other and using them shoddy blue blocks!
This picture shows the connector used at the headlights and the green/grey cable that I cut to provide power to the buzzer circuit. This cable is ONLY on when the headlights are switched to either sidelights alone, or headlights and so ideal for the buzzer.
and the piggyback used with the headlight switch.
Buzzer circuit boxed up, holes drilled to allow the sound out and mounted to the bottom of the kickplate out of the way.
So, I hope this is of some help to someone, as much as it was to me anyway. No more dead batteries!
